Apparatus including fluid support means for magnetic determination of core orientation



July 16, 1968 D. E. WINKEL 3,393,359

APPARATUS INCLUDING FLUID SUPPORT MEANS FOR MAGNETIC TION OF CORE ORIENTATION DETERMINA Original Filed April 27, 1960 4 Sheets-Sheet 1 INVENTOR.

David E. Winkel ATTORNEYS D. E. WINKEL July 16, 196s APPARATUS INCLUDING FLUID SUPPORT MEANS FOR MAGNETIC i DETERMINATION OF CORE ORIENTATION Original Filed April 27, 1960 4 Sheets-Sheet i I ,5: I ,f h1 :t

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INVENTOR. Da vid E. Winkel ATTORNEYS original Filed April 27, 1960 July 16, 1968 D. E. WINKEL 3,393,359

APPARATUS INCLUDING FLUID SUPPORT MEANS FOR MAGNETIC DETERMINATION OF CORE ORIENTATION 4 Sheets-Sheet 5 INVENTOR.

David E. Winkel wwvw ATTORNEYS July 16, 1968 D. E. WINKEL 3,393,359

APPARATUS INCLUDING FLUID SUPPORT MEANS FOR MAGNETIC DETERMINATION OF CORE ORIENTATION Original Filed April 27, 1960 4 Sheets-Sheet 4 MAGNETIC NORTH Figeo.

INVENTOR. Da vid E. Winkel A TTORNE YS United States Patent() This invention relates to the determination of the orientation of core samples taken from the earths crust and particularly to improved magnetic apparatus for the magnetic determination of the direction of alignment of mag- Y netic materials employed in core orientation utilizing the earths magnetic field. This application is a division of a copending application of David E. Winkel, Ser. No. 24,924, filed Apr. 27, 1960, Patent No. 3,209,823, granted Oct. 5, 1965.

Core drilling is employed in various fields and particularly in the mining and petroleum industries in order to secure samples of the earths crust at predetermined depths to secure subsurface geological data for the purpose of analysis and study. Full knowledge of the characteristics of a subsurface formation can be obtained only if the precise location and orientation of the core sample before it was taken can be determined. Many devices, methods and techniques have been employed for this purpose. Some are complicated and time-consuming, some are of limited accuracy, and others have not been entirely satisfactory for various reasons.

Some of these methods for core orientation have utilized the earths magnetic field in effecting the determination of the position of the core sample. One such method employes cementitious material in a fluid state having finely divided particles of ferromagnetic material mixed therein, the mixture being deposited in a small cavity drilled in the bottom of the bore to be cored. While the mixture is still in a fluid state, the particles align themselves with the earths magnetic field and are then locked in their position of alignment upon solidification of the cementitious material. Thereafter the core is drilled and taken with the body of solidified mixture remaining in position in the cavity at the top of the sample and a magnetometer is employed to determine the polarity of the magnetic particles in the core.

The present invention relates more specifically to apparatus employed in the method for determining the orientation of core samples disclosed and claimed in the aforesaid copending application and which employs a fluid mixture of solidifiable material and magnetic particles which may have very high coercive force.

It is an object of this invention to provide an improved apparatus for effectively determining the magnetic polarity of small fragments of matter.

It is another object of this invention to provide an improved portable and rugged instrument for accurately determining the magnetic polarity of small fragments of magnetized material.

Itis a further object of this invention to provide an improved apparatus for determining the magnetic axis or direction of magnitization of materials having high coercive force.

Briefly, in the method of core orientation in which the apparatus of the present invention is employed, a mixture of epoxy resin and finely divided ceramic magnetic material together with an agent for effecting solidification at the end of a predetermined period is provided and before use the ceramic particles are magnetized by subjecting them to a relatively strong magnetic field. The material y 3,393,359 Patented July 16, 1968 to the rock. The core sample is then taken with a drilledout portion of the solidified mixture adhering tightly thereto. At the surface the core sample is marked to provide an identifying line and a small fragment including an identifiable part of the marking is removed and the direction of magnetization or polarity of the particles is determined. The core sample is then marked with the direction of the magnetic field indicating the direction of the North Magnetic Pole of the earth, this being determined by the known position of the fragment with respect to the core prior to its removal.

In carrying out the objects of the present invention in one embodiment thereof an instrument is provided 4for determining the polarity of the fragment removed from the sample which comprises a magnet structure mounted within a case and providing a gap between the opposite magnetic poles within which is arranged a vessel for holding liquid on which the fragment of the solidified material may be floated. An optical system including a reticle for alignment with the markings on the fragment is rotatably mounted about a vertical axis centrally of the vessel and includes an azimuth ring for indicating the angular difference between the direction of the magnetic field of the aligned magnetic particles and the orientation line of the fragment.

The features of novelty which characterize the invention are pointed out with particularly in the appended claims. The invention itself, however, both as to its 0rganization and method of operation, may best be understood upon reference to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a sectional View of a well drill assembly at the bottom of the well in position during emplacement of liquid in accordance with the method employed with the apparatus of this invention;

FIG. 2 is a view similar to FIG. 1 showing the tool assembly Withdrawn from position after emplacement of the liquid;

FIG. 3 is an illustration of the same portion of the well with the tool assembly removed and the coring bit in position during the coring operation;

FIG. 4 is an enlarged view of the liquid charged container employed in t-he equipment of FIG. l1;

FIG. 5 is an enlarged sectional view of the lower portion of the charged container in FIG. 4;

FIG. 6 is a view similar to FIG. 5 showing the container during discharge of the liquid;

FIGS. 7, 8 and 9 are views similar to FIGS. l, 2 and 3, respectively, illustrating coring equipment provided with a liquid charged container shown during three steps in the method employing the apparatus of the invention;

FIG. 10 is an enlarged view partly in section of the coring bit and container of FIG. l;

FIG. l1 is an enlarged sectional view of the lower portion of the container;

FIG. 12 is a plan view of the bottom of the well bore having t-he solidified orientation material in position thereon and illustrating characteristics of the material used in the apparatus of the invention;

FIG. 13 is a view similar to FIG. 12 showing the top of the core Iafter removal and illustrating a step in the use of the apparatus of the invention;

FIG. 14 illustrates a magnetic device for determining the orientation of particles which embodies the invention;

FIG. 15 is a view similar to FIG. 13 illustrating the marking of a core in accordance with its determined orientation;

FIG. 16 is a perspective view partly in section of another instrument embodying the invention for facilitating the determination of the magnetic polarity of particles with a portion of the instrument removed for purposes of illustration;

FIG. 17 is a perspective view partly in section of the optical system and azimuth ring for the instrument of FIG. 16;

FIG. 18 is a sectional view along the line 18-18 of FIGS. 16 and 17 illustrating the optical system in position on the instrument;

FIG. 19 is a plan view showing the top of the instrument of FIG. 18; and

FIG. 20 is a chart for use in the method which employs the apparatus of the invention for determining the angular correction required for cores taken from deflected bores.

In the drawings the invention has been illustrated in connection with apparatus suitable for placing a c-harge of solidiable liquid mixture including a dispersion of magnetic particles at the bottom of the well bore. The liquid is selected to solidify at the end of a known period of time and all magnetic materials are removed from the vicinity of the bottom of the well before the end of this time so that the magnetic particles in suspension in the liquid Will align themselves only with the earths magnetic field prior to solidification of the liquid. After solidification, a core sample is taken, the top end of the sample having the solidified liquid securely adhering thereto.

Various liquid mixtures may be employed in practicing the method employing the apparatus of the invention and the particular mixtures and solidification times are selected depending upon the depth of the bore hole and the nature of the reservoir formation or rock surface on which the liquid is to be solidified and to which it must adhere Securely when solidified. Coloring may also be 4added to facilitate recognition of the solidified liquid on the core. T-he solidified liquid must have the characteristic of adhering securely to the rock or other material to be cored. Various liquids are suitable for mixture with magnetized particles and may -be selected depending upon the requirements of the specific application. It has been found that highly satisfactory results may be secured by employing epoxy resins with a polyamine as the crosslinking or solidifying agent; these resins have the property of wetting rock surfaces and are admirably suited for securing good attachment of the solidified material to the core. Furthermore, while various magnetic materials can be employed and give usable results, it has been found that ceramic magnetic materials commonly known as ferrites are especially useful in the practice of this invention. These ceramic magnetic materials have a high coercive force so that after being magnetized they cannot be demagnetized or remagnetized easily and thus provide substantially permanent records of their alignment after solidification of the liquid. Furthermore, the density of the ceramic materials is substantially lower than that of metallic magnetic substances such, for example, .as iron and alnico particles, and as a result the ceramic materials provide magnetic particles which do not settle as readily in the liquid and therefore may be kept more uniformly distributed in the liquid and provide more uniform and reliable results. Furthermore, the ceramic materials are easily powdered and are particularly suitable to use in a finely divided state which provides the added advantage of greater sensitivity to alignment.

The nature, size and concentration of the magnetized particles are, as indicated, varied to meet the particular drilling conditions. For some applications the particles may be of visible size and may be suiciently large for direct observation; for the purpose of direct observation thc particles may be suitably colored or otherwise marked i and relatively large particles may be marked by color or shape to indicate their polarity. However, for most of the applications herein contemplated, the particles will be of small size and direct visual observation of their orientation is not required.

In order to secure accurate and reliable placement of the liquid mixture at the bottom of the well to be cored, charged containers are provided which include the solidifiable liquid and the magnetizable particles mixed therein. The container is preferably charged with a gas under pressure. When liquids such as epoxy resins are employed, the solidifying or cross-linking agent such as a polyamine may be isolated within the charged vessel by a frangible capsule or diaphragm which may be broken at the time it is to be mixed with the resin, the solidifying time running from the time of breaking the capsule or diaphragm. The magnetizable particles may be magnetized at any time. However, it is preferred for most applications not to magnetize the particles until they are about to be used, whereupon they can be magnetized by passing them through a magnetic field. The concentration of the magnetic particles may be varied according to the requirements of the particular application. However, for general purposes it has been found that a low concentration of magnetic particles provides a very practical type of mixture and avoids a tendency to obscure alignment with the earths field which may result from magnetic interaction between the particles when they are in excessive abundance. For example, a solidifiable substance for the core orienting method of this invention may comprise an epoxy resin with a polyamine solidifying agent (preferably a higher polyamine) comprising the liquid and finely powdered ceramic magnetic material having a concentration of one-tenth to one gram per liter of the liquid. With this mixture, when a solidified fragment is taken from the core it has been found that this fragment may be as small as ten cubic millimeters and still provide an adequate indication of the orientation or polarization of the mass of particles produced by alignment with the earths magnetic field.

For further purposes of illustration and not by way of limitation, ano-ther example of a practical mixture suitable for use in the method of this invention comprises an epoxy resin identied as resorcinol diglycidyl ether with a hardening agent sold by the Dow Chemical Co. as X-2654.4. This composition may be employed effectively with ceramic magnetic materials such as one sold under the trade name Indox-l and the chemical composition of which is BaFe12O19.

For storage purposes the charged containers may be kept cool, which increases the viscosity of the liquid and minimizes or prevents agglomeration of the contained particles. It is particularly desirable to use low temperature storage to keep the viscosity high when the particles have been magnetized before storage.

The solidification time for the liquid mixture may be changed selectively by varying the type or amount of epoxy resin or solidifying agent to provide periods from a fraction of an hour to many hours depending upon the application in which it is to be employed. In the case of charged containers provided with breakable capsules or diaphragms each container may be marked to indicate its solidification period, which will depend on the nature of the resin and solidifying agent employed and the temperature within the particular well bore.

Referring now to the drawings, FIG. l illustrates a drill collar 21 carrying a drilling bit 22 within a well bore defined by walls indicated at 23, the bit 22 resting against the bottom of the bore indicated at 24. Within the collar 21 there is positioned a standard well survey tool 25 including a hollow anchor 26 and a landing shoe 27 secured to the 'bottom end of the anchor and resting in position against a bafiie plate 2S at the top of the bit 22. This particular arrangement of the survey tool in the drilling equipment is commonly known as the bottomlanding type. The devices for emplacing the orienting substance herein described are equally applicable without modification in the survey tool arrangement known as the top-landing type, where the body of the survey tool passes through the plate and is arrested when an enlarged member of the top of the tool contacts the bafile plate.

The hollow anchor is provided with a .charged container and in FIG. 1 a body of liquid mixture 29 has been shown during its discharge through a fluid port 30 in the bit 22. The liquid is discharge through the landing shoe 27 in a manner to Ibe described below. After the` liquid has been deposited as indicated in FIG. 1, the drill assembly isy removed from the area as indicated -in F-IG. 2, the distance of removal being sufficient to present any interference With the effect of the earths magnetic field on the magnetic particles within the discharged liquid.

In carrying out the method of the invention as illustrated in FIGS. 1, 2 and 3, the drill assembly is removed completely fromthe well or )bore and a Corin-g bit is then employed as illustrated in FIG. 3 to remove a core including a portion of the liquid 29 after it has solidified and has attached itself to the bottom of the borehole 24. As shown in FIG. 3, a coring bit 32 is being operated to remove a core 33 from the bottom of the holewith a portion of the now solidified liquid 29 remaining on the top of the core. The coring bit 32 is attached to an outer core barrel 34 in the usual Way and an inner core barrel 35 is provided in the usual way to receive and 4retain the core 33. The material 29 remains securely affixed to. the top face of the core after having been solidified with the magnetic materials dispersed therein. These materials are aligned by the earths magnetic field and provide a substantially permanent record for test purposes. After the core has been brought to the surface it may be positioned in accordance with the previously secured Well data and oriented about its axis by the method of this invention as more fully described later herein.

The construction and arrangement of the charged container within the anchor section 26 of the standard type well survey tool is clearly shown in FIGS. 4, 5 and 6 Where the anchor section is shown containing a charge-d vessel or pressurized cartridge 36. The cartridge 36 and anchor 26 are preferably constructed of a non-magnetic material which may, for example, be a molded synthetic resin or plastic. Other suitable materials include aluminum, magnesium, and plastics having glass fibers incorporated in them, all of which may be drilled away should they lodge in the bore. The cartridge is filled to a predetermined level with the solidifiable liquid 37 and is sealed withva volume of gas under pressure above the liquid. The cartridge may ybe fitted with a standard pneumatic valve 36' through which compressed air or other gas may be admitted to charge the container to the desired pressure.

Before the cartridge is sealed, a frangible or shatterable capsule, diaphragm or other container 41 filled with suitable solidifying or cross-linking agent for the resin or other liquid 37 is positioned in the cartridge and attached to the wall of the cartridge well below the surface of the liquid. This capsule has been shown unbroken in FIG. 4, although in normal use when the cartridge is inserted in the anchor section the capsule would have been broken and the catalyst mixed with the liquid 37 in order to start the solidification period. The capsule 41 .may be broken by a sharp blow against the container.

The lower end of the cartridge is provided with an ar- -rangement for breaking a wall portion of the vcartridge and discharging the liquid when the tool strikes the bottom of the hole. In cartridges having the frangible capsule or diaphragm attached to or near the bottom wall portion of the cartridge to be broken, the solidifying agent will be mixed with the solidifiable uid during the interval of fluid discharge. The details of construction of the wall piercing and fluid discharging device are shown in FIGS. 5 and 6. As shown in these figures, the landing Shoe 27 has a central passage 38 within a tubular fitting 39 which is threaded into the upper portion of the shoe as indicated at 40. 'Ihe shoe is provided with external threads 42 at its upper end so that it can be threaded into corresponding internal threads at the bottom end of the anchor section 26. When the cartridge 36 is to be placed in the anchor section the shoe 27 is unscrewed and the upper pointed end of the tube 39, indicated at 43, is pressed into a fitting 44 molded as an integral partof the cartridge. The fitting 44 is provided with a central opening or chamber below a bottom wall portion 45 of the'cartridge and is provided with intermediate and bottom restrictions 46 and 47, respectively, which have central openings slightly smaller than the external diameter of the tube 39. The plastic material of the fitting is sufficiently flexible to be deformed and afford passage for an annular wedge member 48 on the tube 39 which thus enters the lower chamber formed between the restrictions 46 and 47. The pointed end 43 extends into the upper chamber and lies just below the cartridge wall 45. A second annular wedge 49 is provided on the tube 39 in a position to lie outside just below the fitting 44.

The cartridge with the landing shoe and tube 39 assembled in the fitting 44 is then inserted in the anchor section 26 and the shoe screwed into place at the bottom of the section. The assembly is then dropped or lowered into the drilling tools where it becomes positioned for discharge as Shown in FIG. 1. When the survey tool and anchor 26 strike the baflie plate 28, the momentum of the cartridge presses the wall 45 against the pointed tube which then pierces the wall, the wedge 48 entering the upper shoulder of the fitting and the wedge 49 entering the lower, as indicated in FIG. 6. The shape of the annular wedges prevents their being withdrawn from the cartridge and holds the cartridge and tube in discharging position. The gas under pressure then forces the liquid downwardly through the tube and discharges it onto the surface at the bottom of the well as indicated by the arrows in FIGS. l and 6. Before dropping or lowering the survey tool and combined cartridge into position for emplacement of the liquid it may be necessary or desirable to circulate the `drilling fluid to clear any chips or debris from the bottom of the bore.

After emplacement of the liquid the tool assembly is raised, as stated heretofore, to remove all magnetic material, and when the equipment has been raised the magnetic particles in the liquid are influenced solely by the earths magnetic field and align themselves with the field. When the liquid has solidified the particles are locked in their aligned position and provide a positive indication of the direction of the earths field through the zone at the bottom of the bore, and thus after coring provide this indication on the core which indication is not affected by any turning or twisting of the core during removal.

In the above described embodiment of the invention the liquid emplacing device has been employed with a standard surveying tool lowered in the usual manner through the drill stem or collar and it is thus not necessary to provide a modification of the standard drilling equipment.

The method above rdescribed may also be practiced in connection with standard coring tools by utilizing the pressurized cartridge and without modifying the coring tools for this purpose. FIGS. 7, 8 and 9 illustrate the same three steps of the method as FIGS. l, 2 and 3 but with standard coring tools in all steps. In these gures a standar-d coring tool comprising an outer core barrel 34a having a coring bit 32a is employed, an inner core barrel 35a being arranged to receive the core in the usual manner. A suitable core catching and retaining means such as resilient stepped or shouldered fingers 51 are provided in the usual manner at the lower end of the inner barrel to grip and retain the core.

In this arrangement the charged container or cartridge is constructed substantially in the form of a standard core barrel plug or core marker so that it fits the coring tool and may be locked in place until the emplacement of the liquid has been effected. As shown in FIG. 7, a pressurized cartridge 52 is positioned and locked in the lower end of the coring tool and extends a substantial distance beyond the bit. The cartridge is provided with a discharge device 53 which is actuated upon striking the bottom of the bore 24a and deposits the liquids 29a in a manner similar to that of the first embodiment. The impact on striking the bottom also breaks the lock and allows the cartridge to move back into the core barrel 35a as indicated in FIG. 8 showing the coring bit raised after deposit of the liquid 29a. Then when the well is cored as indicated in FIG. 9 the spent cartridge is moved upwardly in the core barrel in the usual manner of a core marker by the core 33a which is being drilled.

The details of construction of the cartridge and discharge mechanism are shown in FIGS. l and ll. As shown in FIG. the cartridge comprises a hollow container of plastic such as polyethylene or other easily drillable and non-magnetic material which is shaped to .be adapted to the particular type of coring tool with which it is employed. In the illustrated arrangement the core catcher 51 is provided with recesses which receive integral shearing pins 54 formed on the outer wall of Ithe coritainer 52; these pins lock the container in position and prevent its displacement until the unit strikes the bottom of the bore whereupon the contained fluid is elected, as more fully described hereafter, and the pins are sheared off. The cartridge is charged with a solidifiable liquid 55 such as an epoxy resin and a quantity of magnetized ceramic magnetic particles and charged with gas under pressure, as through a pneumatic valve, in the same manner as that of FIG. 4. The cartridge is also provided with a longitudinal frangible diaphragm 56 separating the solidifiable tiuid 55 from the solidifying agent 55'. For purposes of charging, two standard pneumatic valves 52 may be mounted at the top of the cartridge one in communication with a respective chamber on each side of the diaphragm. Thus the liquids are discharged under pressure when the device 53 strikes the bottom of the well ore.

b As shown in FIG. ll, the device 53 comprises a tube 57 having upper and lower wedge-shaped ends 58 and 59 both of which have perforations providing open communication at the two ends of the tube. The upper wedge 58 is flat and is positioned transversely of the diaphragm 56 so that it will cut into both sides of the diaphragm and release both liquids. The tube is secured in position by a collar 61 threaded onto a boss or tting 62 threaded or otherwise secured to the bottom of the container 52. rlhe upper wedge 58 fits in the central opening of the fitting 62 with its point below the wall 65 of the containerarid with its base resting on the collar 61 which holds it 1n position. The tube is also provided with a suitable ridge or key (not shown) to fit a complementary recess (not shown at the side of the opening through the collar and prevent rotation of the tube. A compression spring 63 may be mounted about the tube between the cone 59 and the collar 61 to hold the cone 58 against the collar 61 and minimize the likelihood of accidental puncture of the cartrid e.

'Iie bottom wall of the container is relatively thin as indicated at 65, and when the device 53 strikes the bottom of the well bore the upper wedge 58 pierces the wall 65 and ruptures the diaphragm 56 and allows the liquids 5S and 55 to be discharged by the gas pressure, the liquids flowing through the tube, mixing therein, and out onto the rock surface. The broad base of the wedge 58 holds the wedge within the container during discharge against the pressure in the container which tends to force the tube outwardly.

The modifications of the invention described above may be employed with standard types of equipment as described. In some applications it may be desirable to drop or otherwise deposit a charged container or cartridge into the well after the drilling equipment has been removed and then to lower the coring tools, break the cartridge in position at the bottom thereby releasing the liquid, then withdrawing the tools as before and, after solidification of the liquid, drilling the cores, the cartridge casing being of drillable material and being drilled away in the coring process. The cartridges for this method of operation may, for example, be one of the cartridges 52 of FIG. 7 with the ejection device 53 removed as it is not required when the cartridge is to be broken by the drill. Other forms or shapes and sizes of the charged cartridges may be employed and, for example, may be relatively small spherical cartridges a plurality of which are dropped into the well or admitted with the drilling fluid. Such capsules may also be constructed with sufficient weight added that they will sink through the circulating medium or drilling fluid and settle to the bottom rapidly after the circulation has stopped. These containers which are to be broken by the drilling equipment need not be pressurized. However, pressure ejection and the forced discharging of the liquid will help in many cases to effect better emplacement of the liquid on the surface of the rock to be cored. Also, when employing the plurality of small cartridges, some may contain the resin and ceramic magnetic powder while others contain the solidifying agent, the mixing being effected upon breaking of the cartridges at the bottom of the Well.

After the core sample has been taken with the solidified liquid afiixed to its end, it is necessary to determine the direction or polarity of the aligned particles. FIG. 12 illustrates the bottom of a well bore 24a with the solidified magnetic-particle mixture 29a covering a portion of the bottom. For purposes of illustration the earths magnetic field at the bottom of the bore hole has been indicated by a plurality of parallel arrows 66 pointing in the same direction toward Magnetic North and the particles have been shown as short lines 67 in the material all parallel to the magnetic field or arrows. As mentioned heretofore, the particles may be visible and may even be colored or otherwise marked to indicate their north pointing poles; however, for most applications the magnetic particles will be in minute or powder form. The short straight lines of FIG. 12 nevertheless serve to illusrtate the action with either type of particle.

The alignment of the particles may be determined by testing a very small fragment of the solidified plastic as already mentioned. In FIG. 13, which is a plan view of the central portion of the same rock formation as FIG. l2 after being cut and removed as a core, the core has been shown after the solidified mixture has been marked and is ready for the removal of a circular fragment 68. The core has been marked by drawing a straight line 69 across the top of the solidified plastic and a second short parallel line 70 close to it. The fragment 68 is cut so that the line 70 extends only a sh-ort distance across it to serve as a position indicator. This short line thus identifies the position of the fragment on the core and facilitates correct placing of the fragment when it is returned to the core after determination of its polarity. The fragment is preferably cut or `otherwise removed so that it is taken from a plane substantially at right angles to the taxis of the core.

After the `fragment has been cut from the body of material `it is tested in a simple magnetic device a basic form `of which is shown in FIG. 14. The device provides a body of liquid 72 in a non-magnetic cup or vessel 73 which rests between north-attracting and south-attracting pole pieces 74 and 75, respectively, of a U-shaped magnet 76. The fragment 68 is floated ori the liquid and remains substantially at the middle of the vessel due to surface tension forces of the liquid. The fragment is free to rotate and aligns itself with the relatively strong magnetic field of the magnet, the north-seeking pole of the fragment, as determined by the alignment of the contained magnetized particles, pointing toward the north-attracting pole of the magnet as represented by the arrow 77 indicated on the water surface. The angle between the straight lines on the fragment and the direction of the field is then measured as by observing a protractor (not shown) placed across the rim of the cup 73. For purposes of illustration the fragment 68 is shown in IFIG. 15 replaced to its original position on the core and the magnetic north line 77- marked at the measured angle with respect to the line 69. In actual practice, however, only the angular difference between the lines 69 and 77 Ias described need be transferred to the core; the fragment need not be replaced. Any suitable system of marks or method of marking may be employed, the parallel lines being shown as one suitable and simple method by way of exa-mple. l

An instrument -for facilitating the more precise determination of the direction of alignment or polarity of the particles is shown in FIGS. 16 through 19. The instrument comprises Ia rectangular box having a base 79 of non-magnetic material on which are supported north-attracting and south-attracting magnetic pole pieces 80 and 81, respectively, and a return magnetic path comprising the four side walls 82, 83, 84 and 85 of the case. The poles 80 and 81 are spaced apart and a vessel or vial |87 is mounted centrally in the space between the poles, a ciucular recess 86 being provided in the base 79 to receive the vessel. The case is completed by a non-magnetic cover or top 88 having a circular central opening 89 which receives the upper end of the vessel 87. A ring 91 is fixed to the top 88 concentric with the opening 89 and acts as a seat or retainer for an optical system shown in FIG. 17.

The optical system comprises a vertical tube 92 having a flange 93 which ts on the ring 91 as shown in FIG. 18. The tube and llange 'have been shown-as molded from a single piece of transparent material, the lower face of the flange being stepped or rabbeted to t over the ring 91. A 360 azimuth ring or plate 94 is secured by a small screw 94' to the flange 93 at the stepped portion so that the azimuth ring may be read through the transparent plastic.

A north index line or member 95 is secured to the top of the case at the center line of the north-attracting magnet so that it may register with the marking on the azimuth ring. The optical system is thus mounted so that it may be rotated about a vertical axis coinciding wih the cen-` tral vertical axis of the vessel 87 y The optical system includes a reticle 96 comprising a transparent disc marked with a plurality of spaced lines 97 parallel to the 0-180 axis of the azimuth ring as shown in FIG. 19. A magnifying lens 98 is provided for viewing the reticle when aligning the lines 97 `withmarks on objects such as a floating fragment indicated at 68a which is similar to the fragment 68 of FIGS. 13 to 15. The lens 98 is held on `the tube 92 by a threaded collar 100 and the reticle 96 is secured to the lower end of the tube 92 by a threaded collar or retainer 101.

The liquid in the vessel 87 is selected to provide the required buoyancy of the objects to be floated, and in the case of plastic fragments may be water. The body of liquid lls the vessel to a level fairly close to the position of the reticle to facilitate the registering of the reticle lines with identifying marks such as the line 69a on the fragment 68a. In the illustrated position of FIG. 19 the reference line `69a of the magnetized fragment is at 45 to the center line of the magnetic poles V80 and 81; thus, during solidiiication of the liquid, the earths magnetic field is indicated to have passed through the core from which the fragment 68a was taken at an angle of 45 to the reference line marked on the core. The true line representing the direction of the earths magnetic field on the corre in its original position in the formation may now be marked on the core by drawing a line to the original reference line 69a, essentially the same as the north arrow 77 of FIG. 15, the direction of the 45 polarity line being determined with respect to the fragments original position on the core.

The azimuth ring 94 includes la concentric slot 102 to receive the attachment screw 94', which slot permits adjustments in the positionA of the azimuth ring to allow for minor corrections of alignment with the reticle lines and to compensate for the local declination of the earths magnetic field if desired. Such declination adjustments are usual in survey tools and allow for direct determination of true north rather than magnetic north; however, such adjustments can Ibe used only with cores taken from essentially vertical well bores.

This instrument provides a simple, rugged and accurate device for determining the polarity or magnetic fiel direction of small fragments of solid material.

In the foregoing description of the methods and apparatus for determining the orientation of cores taken from the earths crust, it has been assumed that the core was taken from a substantially vertical well bore. Inpractice the bore or well may lie at very substantial angles of deflection from the vertical. Because the earths magnetic ield may also be inclinedl below the horizontal by widely diEerent angles depending on the location on the earths surface, it becomes necessary whenever the deflection of a bore hole exceeds say 5 from the vertical to introduce a correction in the determination of core orientation by the method of this invention.

Itis common practice in surveying bore holes to determine the amount of deflection from the vertical and the direction of such deflection. This information is thus available from the standard well surveys. 'Il-he amount of correction required for deflected bores may be determined as an angle with respect to the horizontal at which the orientation polarity line, determined as fully described heretofore, marked across the flat end of a core must be set to effect correct orientation of the core. The correction factor can be computed for any magnetic dip and any angle'and direction of the bore hole deflection for use with the orientation method of this invention by means of the following formula:

tan C=(cos I) (tan SMX-5%@ C=desired correction angle in degrees.

1=dellection in degrees of bore hole from vertical near depth of cored rock.

D=dip in degrees of earths magnetic eld Ibelow horizontal at location of well.

S=magnetic direction of bore hole deflection, established as: `0 at east and west, 90 at north, and +90 at south.

FIG. 20 is a chart prepared by using the above equation and indicates the correction factors for a location where the earths magnetic dip or inclination is 70. The chart has been drawn in four quadrants, east of north, west of north, east of south and west of south, respectively. The radial lines thus represent the magnetic compass direction of the deflection of the well bore. r[he amount of deflection of the bore is indicated in degrees by concentric circles and on this chart bore deflections up to 30 are indicated, as designated along the horizontal axis of the chart. The correction factors in degrees as calculated by the formula are indicated by the curved lines. In utilizing these correction factors, the core is positioned according to the data obtained from the well survey and, where the bottom of the bore is deflected in the western two quadrants, the core and Ithe north end of the polarity line are rotated clockwise 'below the horizontal by the amount lof the positive correction factor and couuterclockwise above the horizontal by the amount of the negative correction factor. Conversely, where the bottom of the bore hole iis deflected in the eastern two quadrants, the core and north end of the polarity line are rotated counterclockwise `below the horizontal for positive correction factors and clockwise above the horizontal for negative correction factors. This positions the north end of the polarity line at -the proper rotational position according to the direction of the bore hole deflection with respect to the vertical north-south magnetic plane. The zero correction or horizontal position of the .polarity line on the core is represented by a curved line marked zero in the central part of the uppe-r two quadrants of FIG, 20. All correction factors within these zero arcs are negative and those outside positive.

By way of illustration, a line 105 has been drawn on FIG. 20 representing a bore deiiected north 62 east. The deflection of the bore as determined from well survey data is assumed to be 18, the line thus terminating at the 18 circle. This point ris about halfway between the +20 and +30 correction curves so that a correction factor of -l-25 will be necessary to correct for the deflected bore hole. The orientation polarity line, for example 77 of FIG. 15, is determined as described in detail heretofore and the core is positioned in the attitude of the bore hole as determined from the usual well survey. Since the bore hole is dellected in an eastern quadrant and the correction factor is positive, the core is then rotated counterclockwise about its axis so that the north end of the polarity line is directed 25 below the horizontal, thus completely orienting the core in the position it occupied at the bottom of the deflected bore hole used as an example.

The somewhat egg-shaped zone about the intersection of the north radial line and 20 deflection circle is au area of substantial coincidence of the inclinationor dip of the earths magnetic eld and the bore hole deflection so that the lines of the earths eld run substantially along the core and no reliable indication of direction or orientation of the core may be secured in this zone. When survey data indicate that the well bore is within this zone, it is, of course, necessary to determine the orientation of the core by other methods than relying on the earths magnetic field.

From the foregoing it is readily apparent that the method of core orientation employed with this invention together with the apparatus thereof makes possible a simple, quick and reliable method for` determining core orientation which requires minimum interruption of the operation of the standard drilling or coring procedures or equipment. This method greatly shortens the time for determining core orientation and is readily adaptable to use in the field.

While the invention has been described in connection with specific forms of the method and embodiments of the apparatus, various modifications and other applications will occur to those skilled in the art. Therefore it is not desired that the invention be limited to the specific methods and constructions illustrated and described and it is intended by the appended claims to cover all modifications which fall within the spirit and scope of the invention.

I claim:

1. An instrument for determining the direction of magnetization of a small body of magnetized material comprising a magnet structure including a pair of spaced magnetic poles and a magnetic return path therefor, a vessel of non-magnetic material positioned in the space between said poles, a body of liquid in said vessel, said liquid having a density selected to iloat the material to be observed, means providing an optical system arranged to observe an object on the surface of the liquid in said vessel, said system including a reticle positioned for alignment with an identifying mark on the object to be observed while floating on the liquid, means mounting said reticle above said liquid for rotation with respect to saidyessel about a vertical axis centrally of said vessel7 and an azimuth ring mounted above said liquid coaxially with respect to said vertical axis having markings for reading the angular position thereof with respect to the direction of the magnetic field through said poles.

2. An instrument for determining the direction of magnetization of a small body as set forth in claim 1 wherein said optical system provides magnification of objects floating on the surface of liquid in said vessel.

3. An instrument for determining the direction of magnetization of a small body as set forth in claim 1 wherein said device is mounted in a closed case and said magnetic return path includes magnetic members substantially conforming to the side Walls of said cause.

4. An instrument for deterrniug the direction of magnetization of a small body as set forth in claim 1 wherein said optical system comprises a tubular member having a magnifying lens and said reticle mounted therein and a ange supporting said tube for rotation.

References Cited UNITED STATES PATENTS 2,173,552 9/1939 Franklin 324-56 2,334,393 1l/l943 Dillon 324-13 2,431,666 ll/l947 Fassin 88--1 X 2,634,317 4/1953 Merchand et al. 324-13 X 3,119,185 l/l964 Gray 88-1 X FOREIGN PATENTS 254,307 9/ 1927 Great Britain.

RUDOLPH V. ROLINEC, Primary Examiner.

G. R. STRECKER, Assistant Examiner. 

1. AN INSTRUMENT FOR DETERMINING THE DIRECTION OF MAGNETIZATION OF A SMALL BODY OF MAGNETIZED MATERIAL COMPRISING A MAGNET STRUCTURE INCLUDING A PAIR OF SPACED MAGNETIC POLES AND A MAGNETIC RETURN PATH THEREFOR, A VESSEL OF NON-MAGNETIC MATERIAL POSITIONED ON THE SPACE BETWEEN SAID POLES, A BODY OF LIQUID IN SAID VESSEL, SAID LIQUID HAVING A DENSITY SELECTED TO FLOAT THE MATERIAL TO BE OBSERVED, MEANS PROVIDING ON OPTICAL SYSTEM ARRANGED TO OBSERVE AN OBJECT ON THE SURFACE OF THE LIQUID IN SAID VESSEL, SAID SYSTEM INCLUDING A RETICLE POSITIONED FOR ALIGNMENT WITH AN IDENTIFYING MARK ON THE OBJECT TO BE OBSERVED WHILE FLOATING ON THE LIQUID, MEANS MOUNTING SAID RETICLE ABOVE SAID LIQUID FOR ROTATION WITH RESPECT TO SAID VESSEL ABOUT A VERTICAL AXIS CENTRALLY OF SAID VESSEL, AND AN AZIMUTH RING MOUNTED ABOVE SAIS LIQUID COAXIALLY WITH RESPECT TO SAID VERTICAL AXIS HAVING MARKINGS FOR READING THE ANGULAR POSITION THEREOF WITH RESPECT TO THE DIRECTION OF THE MAGNETIC FIELD THROUGH SAID POLES. 